The invention relates to a shutter mechanism. More particularly, the invention relates to a drum structure in a single-pivot type focal-plane shutter mechanism.
In a conventional single-pivot type focal-plane rotary drum in a camera shutter mechanism, the bottom curtain drum is locked by a pin which is coupled to the bottom curtain drum and is shaped so as to extend into the top curtain drum. It is necessary to form a circumferential groove in the top curtain drum so that the top curtain drum may be turned with the bottom curtain drum locked. It is necessary to limit the angular extent of the circumferential groove to a range of from 200.degree. to 300.degree. in order to maintain the strength of the top curtain drum. Furthermore, it is necessary to set the length of run of each of the top and bottom curtains to values larger than the length of the picture plane opening in order to maintain satisfactory curtain running characteristics. Because of these requirements, the diameter of each of the top and bottom curtain drums must be above a predetermined value.
FIG. 1 shows a conventional rotary drum of a single-pivot type focal-plane shutter. In FIG. 1, reference numeral 1 designates a top curtain drum, 1b a circumferential groove formed in the top curtain drum 1, 2 a top curtain gear, and 3 a top curtain drum shaft. These elements rotate as one unit. Further in FIG. 1, reference character 2a designates a top curtain drum locking pin coupled to the top curtain gear 2, 4 a top curtain drum locking level, 6 a bottom curtain drum, 6a a pin which is coupled to the drum 6 and has a length such that it passes through the circumferential groove and is parallel to the top curtain drum shaft, 6b a bottom curtain drum locking plate having a fork 6d with which the pin 6a engages, 7 a bottom curtain locking lever, 8 a top curtain ribbon, and 11 a bottom curtain.
FIG. 1 shows a state of the rotary drum in which only the top curtain has been run. In order to allow the top curtain to run with the bottom curtain locked or in order that, after the top curtain has been run, the bottom curtain locking lever 7 can be released to rotate the bottom curtain locking plate 6b, pin 6a and bottom curtain drum 6 as a single unit to thereby allow the bottom curtain to run, it is necessary to provide the circumferential groove 1b in the top curtain drum 1. In order to maintain the strength of the top curtain drum 1, the angle of the circumferential groove 1b must be limited to a range of from 200.degree. to 300.degree.. Furthermore, the length of run of each of the top and bottom curtains must have a certain minimum value larger than the length of the picture plane opening in order to satisfactorily maintain the desired curtain running characteristics. From the above-described requirements, the diameters of the top curtain drum 1 and bottom curtain drum 6 are determined.
The recent tendency in cameras is to miniaturize. Accordingly, it is strongly demanded that the interval components of the camera be miniaturized. Moreover, it is also required that yet more mechanisms be accommodated in the space which is provided by reducing the size of the components.
Accordingly, an object of the invention is to provide a rotary drum for a single-pivot type focal-plane shutter which is simple in construction but with which the diameters of the top and bottom curtain drums can be reduced thereby contributing to the miniaturization of cameras and improvements in the functions thereof.